Let's consider the following query:
with
init as (
select 0.1 as y0
),
cte as (
select 1 as i, 1 as x -- x_1
union all
select 2 as i, 10 as x -- x_2
union all
select 3 as i, 100 as x -- x_3
order by i asc
)
select cte.x, init.y0 -- <- ?
from cte
join init
on true
There is a CTE init specifying an inital value y_0 and a CTE cte specifying rows with a value x and an index i.
My question is whether I can write a select which realizes the following simple, recursive formula.
y_n+1 = y_n + x_n+1
So, the result should be 3 rows with values: 1.1, 11.1, 111.1 (for y_1, y_2, y_3).
Would that be possible?
write a select which realizes the following simple, recursive formula.
y_n+1 = y_n + x_n+1
Consider below
select x, y0 + sum(x) over(order by i) as y
from cte, init
if applied to sample data in your question - output is
Note: the expected result you shown in your question - does not match the formula you provided - so obviously above output is different from one in your question :o)
You need to use the “OVER” statement. You can see more documentation about the syntax.
with
init as (
select 0.1 as y0
),
cte as (
select 1 as ts, 1 as i, 1 as x -- x_1
union all
select 2, 2, 10 as x -- x_2
union all
select 3, 3, 100 as x
union all
select 4, 4, 109 as x -- x_3
union all
select 5, 5, 149 as x
order by i asc
)
SELECT *,init.y0 + SUM(i) OVER(
ORDER BY (ts)
) AS res
FROM cte join init
on true
Related
I'm struggling to retrieve a "weighted probability" from a database table in my SQL statement.
What do I need to do:
I have tabular information of probable financial values like:
Table my_table
ID
P [%]
Value [$]
1
50
200
2
50
200
3
60
100
I need to calculate the weighted probability of reasonable worst case financial value to occur.
The formula is:
P_weighted = 1 - (1 - P_1 * Value_1/Max(Value_1-n) * (1 - P_2 * Value_2/Max(Value_1-n) * ...
i.e.
P_weighted = 1 - Product(1 - P_i * Value_i / Max(Value_1-n)
P_weighted = 1 - (1 - 50% * 200 / 200) * (1 - 50% * 200 / 200) * (1 - 60% * 100 / 200) = 82.5%
I know the is not product function in (Oracle) SQL, and this can be substituted by EXP( SUM LN(x))) ensuring x is always positive.
Hence, if I were only to calculate the combined probability I could (regardless of the value I could do like:
SELECT EXP(SUM(LN(1 - t.P))) FROM FROM my_table t WHERE condition
When I need to include the Max(t.Value) I've got the following problem:
A SELECT list cannot include both a group function, such as AVG, COUNT, MAX, MIN, SUM, STDDEV, or VARIANCE, and an individual column expression, unless the individual column expression is included in a GROUP BY clause.
So I tried the following:
SELECT ROUND(1-EXP(SUM(LN(1 - t.P*t.Value/max(t.Value)))),1) FROM FROM my_table t WHERE condition GROUP BY t.P, t.Value
But this does obviously group the output by probability rather than multiplying it and just returns 0.5 or 50% instead of the product which should be 0.825 or 82.5%.
How do I get the weighted probability from by table above using (Oracle) SQL?
Does this do it:
with da as (select .50 as p, 200 as v from dual union all select .50 , 200 from dual union all select .60,100 from dual),
mx as (select max(v) mx from da)
select exp(sum(ln(1-da.p*da.v/mx))) from da, mx;
EXP(SUM(LN(1-DA.P*DA.V/MX)))
----------------------------
.175
with
test1 as(
select max(value) v_max from my_table
),
test2 as(
select 1-(my.p/100* value/t1.v_max) rez
from my_table my, test1 t1
)
select to_char(round((1-(EXP (SUM (LN (rez)))))*100,2))||'%' "Weighted probability"
from test2
RESULT:
Weighted probability
--------------------
82,5%
If you want the calculation per-row then you can use an analytic SUM:
SELECT id,
ROUND(1 - EXP(SUM(LN(1 - wp)) OVER (ORDER BY id)), 3) AS cwp
FROM (
SELECT id,
p * value / MAX(value) OVER () AS wp
FROM table_name
)
Which, for the sample data:
CREATE TABLE table_name (ID, P, Value) AS
SELECT 1, .50, 200 FROM DUAL UNION ALL
SELECT 2, .50, 200 FROM DUAL UNION ALL
SELECT 3, .60, 100 FROM DUAL;
Outputs the cumulative weighted probabilities:
ID
CWP
1
.5
2
.75
3
.825
If you just want the total weighted probability then:
SELECT ROUND(1 - EXP(SUM(LN(1 - wp))), 3) AS twp
FROM (
SELECT id,
p * value / MAX(value) OVER () AS wp
FROM table_name
)
Which, for the sample data, outputs:
TWP
.825
db<>fiddle here
I tried to create a simple SQL to track query_history usage, but got into trouble when creating my timeslots using the table and generator functions (the CTE named x below).
I got no results at all when limiting the query_history using my timeslots, so after a while I hardcoded an SQL to give the same result (the CTE named y below) and this works fine.
Why does not x work? As far as I can see x and y produce identical result?
To test the example first run the code as it is, this produces no result.
Then comment the line x as timeslots and un-comment the line y as timeslots, this will give the desired result.
with
x as (
select
dateadd('min',seq4()*10,dateadd('min',-60,current_timestamp())) f,
dateadd('min',(seq4()+1)*10,dateadd('min',-60,current_timestamp())) t
from table(generator(rowcount => 6))
),
y as (
select
dateadd('min',n*10,dateadd('min',-60,current_timestamp())) f,
dateadd('min',(n+1)*10,dateadd('min',-60,current_timestamp())) t
from (select 0 n union all select 1 n union all select 2 union all select 3
union all select 4 union all select 5)
)
--select * from x;
--select * from y;
select distinct
user_name,
timeslots.f
from snowflake.account_usage.query_history,
x as timeslots
--y as timeslots
where start_time >= timeslots.f
and start_time < timeslots.t
order by timeslots.f desc;
(I know the code is not optimal, this is only meant to illustrate the problem)
SEQ:
Returns a sequence of monotonically increasing integers, with wrap-around. Wrap-around occurs after the largest representable integer of the integer width (1, 2, 4, or 8 byte).
If a fully ordered, gap-free sequence is required, consider using the ROW_NUMBER window function.
For:
with x as (
select
dateadd('min',seq4()*10,dateadd('min',-60,current_timestamp())) f,
dateadd('min',(seq4()+1)*10,dateadd('min',-60,current_timestamp())) t
from table(generator(rowcount => 6))
)
SELECT * FROM x;
Should be:
with x as (
select
(ROW_NUMBER() OVER(ORDER BY seq4())) - 1 AS n,
dateadd('min',n*10,dateadd('min',-60,current_timestamp())) f,
dateadd('min',(n+1)*10,dateadd('min',-60,current_timestamp())) t
from table(generator(rowcount => 6))
)
SELECT * FROM x;
using SQL recursion, I am trying to get a formula from a given set of numbers.
Example, if only 1 number x is provided, the output should be x.
if 2 numbers x and y are provided, then output should be x + y + xy
if 3 numbers are provide, output should be x + y + z + xy + yz + zx + xyz
excerpt:
thanks.
Priya
I'm not 100% sure what you want the result set to really look like. But, you can do this using a recursive CTE:
with vals as (
select *
from (values ('x'), ('y'), ('z')) v(a)
),
cte as (
select convert(varchar(max), a) as a, convert(varchar(max), a) as max_a
from vals
union all
select convert(varchar(max), cte.a + vals.a) as a, convert(varchar(max), vals.a)
from cte join
vals
on vals.a > cte.max_a
)
select cte.a
from cte;
This produces the expressions on each row
This query generates the numbers from 1 to 4.
with recursive z(q) as (
select 1
union all
select q + 1 from z where q < 4
)
select * from z;
But, if I modify it to this,
with x as (
select 1 y
),
recursive z(q) as (
select y from x
union all
select q + 1 from z where q < 4
)
select * from z;
It gives
ERROR: syntax error at or near "z"
What did i do wrong here?
I think this is because RECURSIVE is modifier of WITH statement, not a property of common table expression z, so you can use it like this:
with recursive
x as (
select 1 y
),
z(q) as (
select y from x
union all
select q + 1 from z where q < 4
)
select * from z;
sql fiddle demo
I am having the following problem.
I would like to select a currency value from a database which will act as a default value on the top result of the query (this part is already done and is not a part of my main problem).
I want to use a query that kind of looks like this:
SELECT valkurs, valkurs 'vk'
FROM xx
WHERE valkod='EUR' AND foretagkod=300
UNION
--(My problem is that i can't find out what to write here)
My problem is that I would like to attach a range of values from 1.0 to 20.0 with 0.1 in incremental steps to the original query mentioned above.
An example output can look like this:
8.88, 8.88
1.0, 1.0
1.1, 1.1
1.2, 1.2
...
20.0, 20.0
Is it possible anyhow?
Due to implementation issues this has to be done in a query...
You can use the system table Master..spt_values to generate a sequential list:
SELECT Number = CAST(1 + (Number / 10.0) AS DECIMAL(4, 1)),
Number2 = CAST(1 + (Number / 10.0) AS DECIMAL(4, 1))
FROM Master..spt_values
WHERE Type = 'P'
AND Number BETWEEN 0 AND 200
So to combine in the correct order with your current query I would use:
SELECT valkurs, VK = valkurs
FROM ( SELECT valkurs, SortOrder = 0
FROM xx
WHERE valkod = 'EUR'
AND foretagkod = 300
UNION ALL
SELECT valkurs = CAST(1 + (Number / 10.0) AS DECIMAL(4, 1)), SortOrder = 1
FROM Master..spt_values
WHERE Type = 'P'
AND Number BETWEEN 0 AND 190
) T
ORDER BY T.SortOrder, t.valkurs;
ADDENDUM
There are some that do not advocate the use of Master..spt_values due to the fact that it is not documented, so it could be removed from future versions of sql-server. If this is a major concern you can use ROW_NUMBER() to generate a sequential list (using any table with enough rows as the source, I have gone for sys.all_objects):
SELECT valkurs, VK = valkurs,
FROM ( SELECT valkurs, SortOrder = 0
FROM xx
WHERE valkod = 'EUR'
AND foretagkod = 300
UNION ALL
SELECT TOP 191
valkurs = 1 + ((ROW_NUMBER() OVER(ORDER BY object_id) - 1) / 10.0),
SortOrder = 1
FROM sys.all_objects
) T
ORDER BY T.SortOrder, t.valkurs;
Old, but I think some people will benefit from my answer, which is a much better implementation than the accepted answer
WITH e1(n) AS
(
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL
SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
), -- 10
e2(n) AS (SELECT 1 FROM e1 CROSS JOIN e1 AS b), -- 10*10
e3(n) AS (SELECT 1 FROM e1 CROSS JOIN e2), -- 10*100
numbers as (SELECT n = ROW_NUMBER() OVER (ORDER BY n)/10.0
FROM e3)
select n, n from numbers
where n between 1 and 20